This interesting liquid product can be, at times, a good substitute for
critical point drying CPD, especially for those laboratories not having
available a good critical point
dryer. Because of its
generally rapid infiltration, it is ideal for the preparation of insect tissue. However, do not expect
the results, in general, to be as one would get with the use of a good
critical point dryer. Remember, we "recommend" the use of
Hexamethyldisilazane only when a good operating CPD unit is just
not available. Until recently, the main application for HMDS has been in
life science microscopy but in more recent years, interesting applications
in materials science have been found.

Who would find the HMDS approach useful?
Workers who are doing their SEM examination at relatively low magnifications
or are working with samples, known to not possess any fine structure that
would otherwise be seen at the magnifications of interest would probably be
those most likely to find the HMDS generated results to be the most
acceptable relative to critical point drying. For example, excellent
results have been reported for pollen in the publication:
"Hexamethyldisilazane as a Drying Agent for Pollen", Biotechnic &
Histochemistry 69, 192-198 (1994).

Known limitations of HMDS:
Naturally, the seriousness of these limitations might be in the eyes of the
beholder. But we would point out that when HMDS is used (instead of
critical point drying), one does experience shrinkage of tissues, especially
of connective tissues. HMDS is caustic, and flammable, and should be used
only in a fume hood. Some might characterize the use of HMDS as being
outright "nasty" when compared to the use of CPD.

Other miscellaneous information:
For relatively larger samples, the quality of the final result can be
enhanced if the final dried sample is put in a vacuum oven at 55-60°C for
several hours to be certain that that sample is indeed completely dry before
gold coating, prior to SEM examination. If moisture is still diffusing out
of the sample during sputter coating, not much gold will deposit and the
sample will end up without the desired surface conductivity.

Silanization of glass surfaces:
Glass microscope slides can be made hydrophobic using SPI-Chem HMDS. The
procedure is simple and works quite well. Place the slides, separated, in
a wide mouth glass jar preferable with a PTFE lined cap. Add a few drops of
the HMDS which will then vaporize in the sealed jar reacting with the
surface of the slides. Better results are obtained if this is done while
keeping the jar at 70° for twelve hours, but with the cap slightly ajar.

At the end of the twelve hours, remove the slides. Water droplets will now
"bead up" on the slide surfaces. The layer responsible for the hydrophobic
behavior with we less than one nm in thickness and will also be completely
invisible to the eye.

Applications in semiconductor technology:
HMDS is an outstanding adhesion promoter especially in terms of improving
the adhesion of photoresist to the wafer surface. It is deposited on the
wafer surface prior to the deposition of resist.

New applications in nanotechnology:
The preparation of non-interacting and non-touching nanoparticles is one of
the biggest challenges faced by workers in this exciting new field of
research. Hence, for those interested in the controlled synthesis of
non-aggregated nanoparticles with diameters between 1 and 50 nm,
one can synthesize nanosize SiO2 particles from hexamethyl-disiloxane
(HMDS) as precursor and oxygen as the oxidizing agent.